Thermal airflow sensors have conventionally been a mainstream airflow sensor that is installed in the intake air passage of internal combustion engines, such as those of automobiles, to measure intake air volume since the thermal airflow sensors are capable of directly detecting amount of air.
Recently, there has been developed an airflow sensor formed by having resistors and insulating layer films deposited on a silicon substrate by use of semiconductor micromachining technology, part of the silicon substrate being removed thereafter by a solvent represented by KOH to form a thin-wall portion. This airflow sensor is drawing attention because it has high-speed responsiveness and is capable of detecting counter flows thanks to its quick response. In recent years, for the purpose of reducing the number of components constituting the substrate portion (printed substrate, silicon substrate, etc.), study has been underway to prepare a resin package integrating a flow rate detection element and other components, the package being formed by mounting the flow rate detection element, circuit board, etc., on the same lead frame and by sealing the periphery of the frame in resin through the injection molding process.
Meanwhile, where semiconductor circuit elements such as LSI and microcomputers are to be sealed in resin, the circuit elements and the lead frame are often bonded together by use of sheet adhesive. The general method for using sheet adhesive involves pasting the sheet adhesive onto the back of the semiconductor circuit wafer and having both the wafer and the sheet adhesive layer cut into individual chips in the dicing process so that the entire backs of the semiconductor circuit chips will carry the diced sheet adhesive layer. As a result, the individual semiconductor circuit elements can be mounted as they are on the lead frame, which offers the advantage of eliminating the process of printing solvent over the elements as when a solvent-based adhesive is used.
The invention described in Patent Document 1 involves bonding an electronic element with a support substrate. Patent Document 1 discloses that multiple openings each having a predetermined area in planar view are formed in an electronic component adhesive sheet for fixedly bonding the electronic component with the mounting base. According to Patent Document 1, it is possible to prevent a convex formation caused by inclusion of air bubbles between the electronic component and the sheet adhesive being bonded together, which improves the adhesion between the mounting base and the electronic component.